CNG pump compressor DIY home refueling

[vlad]

Originally Posted by cRiPpLe_rOoStEr

Any of the major players in the CNG kits industry have multipoint injection kits, which we know in my country as "positive pressure" systems.

I had Landi Renzo Omegas Propane injection system on my Astro van. It was running just like your regular gasoline system.

When you have MPFI gas system it is kinda stupid to install propane /methane carburetor.....

For diesel vehicle propane/methane is your "secondary" fuel system, so again multiport injection is the best but even a single electronically control feed valve will give very good results.

[cRiPpLe_rOoStEr]

Originally Posted by vlad

For diesel vehicle propane/methane is your "secondary" fuel system, so again multiport injection is the best but even a single electronically control feed valve will give very good results.

But why would we want to downgrade?

When you have MPFI gas system it is kinda stupid to install propane /methane carburetor.....

Tell that to taxi drivers in my hometown. Many of them still use even the so-called "aspirated" or "faucet" kit, not electronically-controlled, in spite of it being illegal for cars made after '97.

[vlad]

I was thinking again about "first compression stage". My choice was Copeland R22 compressor or York 210 AC compressor. Both have pros and cons.

Copeland performs great, has motor built-in reliable but suction pressure is low and gas is "warm" compare to refrigerant. Also Refrigeration oil is very hygroscopic (mineral oil is less but still).

The problem with this oil is it becomes acidic and this acid eats motor copper (not good at all). When this compressors used in closed refrigeration system you remove as much water as possible by pulling deep vacuum for few hours and you have filter/drier which kills the rest of water. In my application I will always have "fresh gas" I have no idea how dry it is.

To put just a compressor oil in it? I don't know how scroll will like it and again motor windings are cooled by this oil and I don't know how wire insulation will like it or not....

Also I would like to keep electric parts out of gas as much as possible. With this compressor gas goes around windings. May be I am just a frick but I saw enough burned out compressors....

York is on other hand is just a bare compressor. It accepts w30 non detergent oil which is cheap and non hygroscopic (even engine oil can be used). This compressor is a high volume compressor. I need to turn it only about 700 RPM to get 2 GGE /hour. At this speed it spits less oil about 1 oz /hour. This oil will help to lubricate "second stage compression". The only one problem I can see right now is I will need to find sealed electric motor.....

I bought one York 210 compressor on eBay today, I will need to determine power of electric motor for it. I have few electric motors lying around I know compressor RPM, Max pressure, so I will need to check motor amperage and this will give me power. Easy enough. When I know motor power I will buy a sealed one....

Here is great info about York 210 compressor:

http://www.worldaire.com/pdf/Worldai...ompressors.pdf

[P-hack]

If you are bent on 3600 psi then why not use oil as a piston like I mentioned? You can use it with a direct injection pump off an old diesel or any of a myriad of inexpensive hydraulic pumps or combination of high flow/low flow (high psi) pumps. To pump gas at high pressure, the demands on machining precision go up significantly and maintenance goes up as well (and price)., plus "stages" become necessary. A hydraulic pump can run for years, and solves lots of other "sealing" and separation issues.
3gpm@1800rpm, $100
Hydraulic Gear Pump GP F10 6 1 P C 3625 PSI 4000rpm New MP Filtri JP | eBay

Even that little pump will squish 127 cu feet of gas to 3600psi in 5 hours at modest rpm. Just need a high pressure accumulator tank (a tank with a top and bottom outlets would do) and some valves and a controller.

3 valves/solenoids,
1. closes off gas outlet
2. closes off hydraulic fluid return to storage
3. closes off low pressure natural gas supply
operation:
A. start/reset:
close 1, open 2 and 3. Incoming gas forces fluid back into storage.

B. when fluid is at correct low level in accumulator:
close 3 and 2, open 1 and turn on pump. Stop process when correct pressure is reached.

C. When fluid is at correct high level, go to A and reload accumulator with gas.

Main compromise is between solenoid switching life and accumulator size/cost.

Do you need a membrane/floating piston in the accumulator? Or does hydraulic fluid not care if it is next to methane? Either way, oxygen is a no-no in any cng system.

[vlad]

Originally Posted by P-hack

If you are bent on 3600 psi then why not use oil as a piston like I mentioned? You can use it with a direct injection pump off an old diesel or any of a myriad of inexpensive hydraulic pumps or combination of high flow/low flow (high psi) pumps. To pump gas at high pressure, the demands on machining precision go up significantly and maintenance goes up as well (and price)., plus "stages" become necessary. A hydraulic pump can run for years, and solves lots of other "sealing" and separation issues.
3gpm@1800rpm, $100
Hydraulic Gear Pump GP F10 6 1 P C 3625 PSI 4000rpm New MP Filtri JP | eBay

Even that little pump will squish 127 cu feet of gas to 3600psi in 5 hours at modest rpm. Just need a high pressure accumulator tank (a tank with a top and bottom outlets would do) and some valves and a controller.

No, I don't want 3600 PSI... This is too much for DIY and will require more precise equipment.

Let's see how "second stage" will work:

Let's assume you compressed gas to 200 Psi with compressor. Easy enough, right? You only need single stage compressor. In my case York 210.

Now I need 1200 Psi. Is it too much? not really. 1200/200=6 times compression not really a rocket science... but

Here it gets tricky. To make compression efficient you have to squeeze gas and leave as less room as possible when you retract piston or diaphragm or whatever you use.

Let's put it this way: You have cylinder/piston. when you squeeze it, gas will overcome pressure at discharge valve (check valve) and go somewhere (your fuel tank etc). All gas that is left in cylinder will re-expand and your 1 stage will have to fight with it's pressure. This is your efficiency loss. Your goal is to leave as less gas as possible after each stroke.

I am thinking about using oil as "filler" Oil will lubricate cylinder and "fill" voids, so gas will have no room left for re-expansion Excess oil will get to oil separator and I will drain it once in a while.

What to use diaphragm or piston/cylinder is a personal choice. Hydraulic cylinder is good for 10 million cycles (this is like 10-20 years of every day use). This is ideal but even if I need to change seals every 3-4 years ($30-$40 set and 1 hours of labor) this is really nothing compare to $2000 every 2-3 years bill for rebuilding 4 stage CNG compressor like Phill.

I was thinking about having hydraulic cylinder with gas on one side and hydraulic oil on the other side but I don't know what will happen in case if gas leaks to oil side?

I will have 2 cylinders one is gas (both sides) and the other is hydraulic ram(both sides). Hydraulic ram will push/pull gas cylinder. When gas is compressing on one side the other side will expand and will be filled with gas by "first stage".


Now potential leaks:
If oil leaks from hydraulic ram I will see it. If gas leaks at piston this will extent compression time. There is only one place where gas can leak out. This is failed rod seal. If gas start leaking at rod seal It will pull oil with it and I will be able to see this during inspection.

Also as an additional safety I want to put gas detector which will shut down everything.

[vlad]

If you use 2 compression chambers (2 hydraulic accumulators or 2 sides of cylinder) you can cycle hydraulic oil from one to another. In this case you don't need to start/stop hydraulic pump. You don't need to control gas flow you only need check valves.

Also I didn't get how you want to retract diaphragm? Your gas supply line is max 2 psi. It will take forever to retract diaphragm and push hydraulic fluid back. You can push/pull cylinder but you only can push diaphragm.

Also as you mentioned oxygen is no no. I absolutely agree oxygen is your first enemy. This is why I want to use 1 stage to get 200 Psi. In this case gas will always want to escape and you will never pull air=oxygen in your system. If you use piston to pull gas which is at very low pressure you will get to vacuum and if your seal leaks you get air in....

So, I think 1 stage is kinda unavoidable for less pumping with 2 stage and for keeping air out...

[rmay635703]

Originally Posted by P-hack

If you are bent on 3600 psi then why not use oil as a piston like I mentioned?

I am wondering if any of the ANG tanks are dual pressure compatible? I have seen it "mentioned" on one of the japanese manufacturers of ang tanks but they don't list any product numbers.

Reason being I would like the smaller size of ANG and lower pressure but also would like to be able to top off. I have never found a decent ANG tank domestically, I wonder if one exists like this?

If so I could stick to a relatively low pressure unit for home use (500psi) but have the tank capable of withstanding a quick fill from a local CNG fill station.

Ah well.

[vlad]

Originally Posted by rmay635703

I am wondering if any of the ANG tanks are dual pressure compatible? I have seen it "mentioned" on one of the japanese manufacturers of ang tanks but they don't list any product numbers.

Reason being I would like the smaller size of ANG and lower pressure but also would like to be able to top off. I have never found a decent ANG tank domestically, I wonder if one exists like this?

If so I could stick to a relatively low pressure unit for home use (500psi) but have the tank capable of withstanding a quick fill from a local CNG fill station.

Ah well.

I personally don't see serious CNG - ANG alternatives in the nearest future. The technology is too darn simple and with home fueling makes is cheap. At this point HUGE unreasonable cost of home CNG pump kills it all. Commercial vehicles? may be....

Do you think car-maker's first priority is your wallet? Don't be naive.... money.... is their priority number one....


Just look were all car manufactures moved...... hybrids. Why? because they can "JUSTIFY" extra cost to you. Most hybrids have pay off period 10+ years and at that point you need new battery which wipes off your "savings". Taxi....? sure home use 10-15K a year? No

I see this as help yourself DIY project.

I think "dual pressure" has no sense from commercial point of view. You need strong 3600 Psi tank and if you have it they will sell you high pressure pump $$$$$$.

Now I am back from "no internet" vacation. My York 210 compressor just arrived, hydraulic cylinders are here... Fun begins.....

[rmay635703]

Originally Posted by vlad

I personally don't see serious CNG - ANG alternatives in the nearest future. The technology is too darn simple and with home fueling makes is cheap. At this point HUGE unreasonable cost of home CNG pump kills it all. Commercial vehicles? may be....

Now I am back from "no internet" vacation. My York 210 compressor just arrived, hydraulic cylinders are here... Fun begins.....

No offense but ang tanks are used all over the world, there is no reason that you could not import one, if you were to determine the company and contact info.

No pipe dream, US just doesn't use the things much.

[vlad]

I just keep getting hydraulic parts. I decided to use arduino as a control module. Using it allows to control just about anything.